Rats, mice, and other rodents are undesirable in human habitations, work places, and agricultural areas. Rodents are commonly exterminated by placing bait units consisting of food impregnated with a rodenticide in areas frequented by rodents. If the rodents can be made to consume the rodent food or bait, they will take the rodenticide as well and will die shortly thereafter.
To be effective, the bait units must be attractive and palatable to the rodents. Rodent bait has been formed in the shape of seeds, as in U.S. Pat. No. 944,419; in the shape of tablets or cylindrical cakes as in U.S. Pat. No. 962,886; and in the form of chunks or crumbs as in U.S. Pat. No. 3,223,231. Bait in very small units has the advantageous property that it fits easily into a rodent's mouth, facilitating rodent consumption of the bait. However, bait in a powdered form or in very small chunks has the drawback that it tends to flow when placed, or be easily dislodged from the baited area. Small bait crumbs can be blown away by winds, can easily be brushed aside or trampled by the rodents, or can be washed away by rain or run-off.
Bait of a small particle size is also more difficult to apply, requiring the user to measure and dispense the bait or place it in a bait container. For these reasons, larger chunks or cubes of bait are often employed. These larger chunks have the advantages of ease of placement and measurement as well as being more stable in their positioning. However, a bait cube on the order of one inch on a side is very large with respect to the mouth of a rodent. As a result, rodents find it difficult to consume the bait, resulting in unused bait or in rodents consuming less than a fatal quantity of rodenticide.
It is also desirable to have a bait unit which can withstand rain, snow, and humidity without rapidly becoming rancid, and hence unpalatable to the rodent. Baits containing high fractions of paraffin show increased weather-resistance, but suffer a commensurate loss in palatability.
What is needed is a rodent bait which is large enough to be conveniently handled and placed, yet which remains palatable and accessible to a rodent. A bait which retains its palatability despite exposure to varying weather conditions is also desirable.